Method and apparatus for extruding rubberlike material



Oct. 7, 1952 o. MATHUES 2,612,655

METHOD AND APPARATUS FOR EX'I'RUDING RUBBERLIKE MATERIAL Filed NOV; 4, 1948 INVENTOR.

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H/s Arm/Wm Patented a. 7, 1952 METHOD AND APPARATUS FOR EXTRUDI'NG;

RUBBERLIKE MATERIAL Thomas 0. Mathues, Dayton, Ohio, assignor to General .Motors Corporation, Detroit,- Mich, a;

ccrporationof Delaware Application November 4, 1948;S'eria1iNo. 583 208"? This invention relates-- to extrusion machinesand" method of extruding rubber-likematerials and is particularly concerned withapparatus and methods forextruding crumb stock.

It-is further the basicobject 0f -the;inventi0nto provide amethod and machine ier-extruding crumb stock" directly without any-preliminarywarmingupof the crumb or otherwiseplasiucizingthe-same-priortoits useinthemachine.

In-- carrying out the above object; it; is; afurther-- object to provide an extrusion die-consist ing of aplurality -of nozzles,- the-flrst of'which coniprises-a plurality otaperture -of re1atively-- small size, preferably spaced adjacent-the outerperiphery of the nozzle; so that; the crumb stock as ibis-fed throughthe nozzle" by action of the extruder-screw, is brokengup -into aplurality of small streams or-threads; The output of this first nozzle is led through a tapered" bore intoanother nozzle-which; preferably,- is of less cross sectional area-thanthe-tctal cross sectional area of the -plu-rality-- of-apertures in the first nozzle. As'the-threads of extruded crumb pass'iromthe first nozzle into the tapered bore, they are mechanically worked and thereby-"plasticized' and;

afterpassi-ngthrough the second nozzle, are integrated into a single stream or thread which is ofgood strength -uponcuring and consists of a satisfactorily-extruded shape: If the shape of the-extruded article is atall complicated-in itscross section,- it is desirable toprovide a: third nozzle which carries this desired configuration: Thisthird-nozzle also has a taperedboreltaading intothe ingress end thereof and the cross sectional' area of the nozzleper se-which carries the configuration of the crosssection-oi theextruded article is preferablyofslightly less area-than-the area of the preceding nozzle.

Azstill further-object of theinventicn is to provide: a v method for mechanicallyplasticizing and working crumb stockin an extrusion head whereby an extruded length of rubber-like material may be-produced without warming: up the crumb priortoits introduction inthe extruder.

Further objects and advantages Of the present invention will be apparent from the following descriptiom reference being had to the accompany-mgr drawing, wherein" preferred embodimentsoi the present invention are clearly shown;

Inthe drawing Fig. l' 'isa diagrammatic view of an extruding machine.-

Fig; 2 is a-view in crosssection of an extrusion headior-said machine. I Fig. 3 is a view-taken-oxriinei 'orFig; '2':

Fig. 4 is a viewtakencn'lineda-moiii ig: 2: Fig. Eris a view taken on line"5 -5 of Fig-'-. 2.

Theuse of rubber-like crumb-stochhasbecome v increasingly important since the-introductiOm-of synthetic" copol-ymers.- Rubber-like copolymerm may be made in crumbform quite easilyr form of stock presents -ahighly -satisfactory ma-- 4 terial from a handling standpoint, the stock--is dr: and free fiowingand may-be shoveled or conveyed from-onepoint to another; thereby obviat 3 ingpast diflicultiesin the-useof rubber-likema-eterial wherein slabs-and/or sheetsvmust necesesarilybe-conveyed. v

Butadiene-styrene copolymersybutadiene-acry lonitrile copolymers and polymereof othencompounds containing a single ethylenicdoubl-bond C=C which are copolymerizable witlrbuta-- dime-1,3; hydrocarbons irraqueoussuspensions all may be used; Also any other rubbenor' rubber-like material thatwill-form-a crumb-of satisfactory nature. This crumb has never tie-=- fore beerrof a satisfactorwnaturefor-use in extrusion' machines.

machine; This has beeneliminatedto a large extent by changing the design ofithescrew"and= the hopper or by-usingatamper. However; even when the machine is madeto feed the crurnb-, satisfactorily, the output orthe-extrusion--di e-or-- head is of a crumby nature: and has very -lowtensile strength and-in manyinstances ;bre aks-ofi as itcomesfrom the die; Thus;in-orderto-make satisfactory extruded articles, ithas-been-neces sary -in the past to-warm' ne -the crumb rubber: by I mechanicallypre working; the stock' on hot'" "1 rolls or in a-knea'ding machin'erv 'Ihisobviously is an expensive procedure-and to some extent; nullie fies the other advantages: in? the use off? crumb, stock;

I have found that through a unique desi n. 01miextrusiondie-to be used'on anextrusion machine, or tuber as it is often called; thatthegdifficulties, heretofore experiencedmay be eliminatedgin their entirety'and'that crumb stock maybe fedidirecte 1y to the hopperoftheptubervand;extrudedir'omr the die end thereof in long lengths of high yde-w sirable material' having tensile ,strength'. aDDIOxi-gmatingand/or equalto the strength oifg'extrud'edif milled rubber-like-material;

I have found that this diedesig n iscriticaLandQ must-be followed rather closely in orderto obtaini satisfactory results. invention; reference to the drawingswfl]; bamade.

-wherein- Fig: i'shows' a tuber or extrusion ma:

Thedifiicultiesexperiencedare-manifold. First; d-iificulty--is experienced in I conveying" the crumbwithin; the screw" ofthe 0 more. ,fullyr e plaining chine at ZU-including a feed hopper 22, ascrew housing 24 and an extrusionhead 26. The machine is driven by a motor 28 through a gear box 30. Crumb stock fed into the hopper will be conveyed through the screw housing 24 to the head or die 26 whence it will emerge in the form of a tube, rod, etc., at 32.

Explaining the unique design of the extrusion head or die more fully, it will be seen that in Fig. 2 the die 26 comprises three main sections 34, 36 and 38 held to the housing 24 by a plurality of bolts 40. A screw within the housin ,24

, is shown at M and this acts as the conveying means for the crumb from the hopper 22. The die part 34 is shown in plan view in Fig.

3 wherein the main face of the part 34 is undercut by means of a drill ground to a substantially right angle as at 42. This taperedbore is further undercut as at 44 by smaller drills and then each of these undercut portions is provided with an aperture46 which passes completely through the part 34. In the'embodiment shown in Fig.3, four of such apertures are provided. It isto be understood that more of said apertures may be used if desired and that the number may even be reduced to two in some cases, although three or more are preferred for'reasons to be discussed hereinafter.

The outlets of the; apertures as feed into a tapered-bore 48 in part 36 which acts as the inlet for an aperture 50 therethrough. The aperture-U is preferably of a size slightly less in cross sectional area than thetotal cross sectional areas of all the apertures 46. In this manner, theoutput of the apertures 46 is fed into the bore-48 andis compressed slightly asit is mechanically worked through high turbulence, thereby introducing heat into the operation. During this step. the velocity of the extruded materialis increased to cause additional heating efiect. It has been found'that the output of the aperpart and feed into a tapered portion whereby the separate streams are turbulently worked, being caused to fold over one another under compression prior to passage through the next aperture as at 58. It is apparent here that if only two apertures 46 are used that similar results may be obtained by using another die portion 36 which is drilled for two apertures at right angles ture is asatisfactory extruded article having good tensile strength and satisfactory finish. In some instances, however, where the 1 cross section of the extruded shape is more or less complicated in configuration, it may be desirable to add a third die part 38 which also includes a tapered inlet bore 52' and a properly shaped aperture 54,

which aperture 54 includes the final shape of the desired article in cross section. Aperture 54 is preferably chamferedat its outlet as at 56 and here s am, the cross sectional area of the aperture, 54 is preferably slightly less than that of aperture 50 to create a build-up of pressure within the. bore 52-,therebyadding still further heat through mechanical work due to the turbulence ofv the material being passed therethrough.

The principle behind the operation of this tubing die, as it may be termed, rests in the me chanical work introduced into the material due to being broken up into a plurality of small streams which are fed inwardly to a central point and. are placed under a degree of compression for introducing heat. Thus, the tubing die 2B'actsin a degree the same way as the milling operation previously used in the art. In other words,the mechanical working and warming up ofv the crumb stock is accomplished directly within the die, thereby eliminating the f necessity of external operations.

It will be noted that in die part 34 the three or rnore" holes or apertures 46 which are used in the'prig'inal breaking up of the crumb stock are pa fad;acentv thefouter periphery of the die to those in the first die part and then adding a third die within a single aperture therein. In other words, any number of variations of the principle may be usedto accomplish the same end, the basic principle behind the Whole operation being to break up the crumb into a plurality of small streams of rubber-like material and to take these small streams and fold them over one upon the other in a turbulent manner for causing mechanical working of the stock together with the generation of heat after which the mechanically worked and heated stock is passed through the extrusion-die to form a final shape. This principle is the basis of my invention. It must also be'noted that the apertures;

at 46 must be out of line with aperture 50 so that the streams of the rubber-like material are caused to change in direction during progress through the die ZEi. Otherwise the moving material will pass through in a stream from one die final die will not have any strength. In fact,'

this very actionis apparent when using a strainer inthe tuber and passing the output of the strainer into an extrusion die. In this instance, only that portion of material in direct line with the die moves through the strainer and the remainder thereof stays inactive within the extrusion head. This is the peculiarity that is inherent in crumb when being forced through a die 7 by means of a screw or other pressure feed. It is apparent from the design of my improved head that all material within the die must move since it is constantly being broken up and directed to, a different point which is out of line with the, output end of the preceding die part, thereby eliminating any dead portions within the charge. I have found that the balance between the cross sectional area of the apertures in part 34,

and part 36 are not of any great importance, al-

though the aperture inpart 36 is preferably no greater in cross sectional area than the total cross sectional areas of the apertures in part34; and preferably-should be: slightly less to cause-a back pressure which creates additional heat;

The use of thehead or die 38, as previously men-'- tioned, is not entirely necessary unless a complicated configuration of the article is desired and even'in this case, it may be eliminated in I This had best be arrived at by many instances.-

trial.

The exact size of aperture 50 with respect to aperture 46 is also best arrived at by trial. When extruding or tubing a butadiene-styrene copolymer compound, it was found that the cross sectional area of the aperture 50 to give best results,

should be exactly one-half the area of .thetotal cross sectional area of apertures 46. However, as the formula changes, satisfactory results may be obtained with otherarea evaluations and, for

that matter, even with the aforementioned stock I satisfactoryextruded shapes were made wherein the aperture 50 was but slightly less,-for example,

5% less than the total area of the apertures 46,

From the foregoing it is manifest that I have provided a new method and apparatus for tubing or extruding crumb stock directly without any warm up worktherein external of the tuber. It is to be understood that any crumb stock of rubber-like nature may be satisfactorily extruded by this method and in this apparatus, providing such crumb stock can be extruded in conventional apparatus after a warm-up. Therefore, the method and apparatus is in no way limited to the use of ity of small streams, changing the direction of flow of said streams and then integrating the streams into a single stream is maintained.

Also, although the orifices shown are substantially round, it is manifest that any geometrical design of outlet may be used in the various dies providing the other factors are maintained.

This apparatus and method is also applicable to mill mixed stock wherein the stock may be extruded without warm-up which is required under usual extrusion procedures. Also, the mill stock can be used in ribbons, shreds, or any other form.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. Apparatus for extruding rubber-like crumb stock, comprising in combination; a tubular having a pressure feed screw, a tandem die adapted to receive the crumb stock under pressure from said feed device, said die consisting of at least two portions, the first of which includes at least three orifices of relatively small size radially.

spaced, said orifices being disposed circumferentially and substantially tangent to a circle defined by the outer diameter of the screw, and the second portion of which consists of a tapered inlet having a throat opening connecting with the outlets of said orifices in the first portion and tapering down to a single opening therethrough which is substantially centrally located and out of line with respect to any of the orifices in the first portion and which has a cross sectional area at In all cases, the principle of breaking up the crumb into a pluralleast 5% less than the total cross sectional area of the orifices in the said first portion, whereby stock passing through the orifices in the first portion is broken up into small streams which are folded and worked into a single stream which passes through the final orifice.

2. Apparatus for extruding rubber-like crumb stock, comprising in combination; a tuber having a pressure feed screw for feeding crumb stock therethrough, and a tandem die disposed at the outlet end of said tuber and adapted to receive said crumb stock under pressure, said tandem die consisting of at least two portions, the first of which includes at least three orifices radially spaced, said orifices being disposed circumferentially and substantially tangent to a circle defined by the outer diameter of the screw, and the second portion of which includes a tapered bore leading from said first portion orifices to a substantially centrally located single orifice and out of line with respect to any of the orifices in the first portion wherein the cross sectional area of said centrally located orifice is approximately one-half the total cross sectional area of the orifices in the said first die portion.

3. In the method of extruding rubber-like crumb stock, the steps consisting of; conveying cold crumb stock under high pressure by means of a screw directly to an extrusion head in a single stream, breaking said stream of crumb stock into at least three relatively small streams of material said streams being radially spaced and circumferentially disposed so as to be substantially tangent to a circle defined by the outer diameter of said screw, plasticizing the stock in said small streams by causing the same to be heated through folding by changing the direction of flow of said streams toward a common center whereby high turbulence is created, integrating the small streams into a single stream wherein the cross sectional area of said single stream is at least 5% less than the total cross sectional area of said relatively small streams whereby the stock is extruded under high pressure into a well integrated mass.

THOMAS O. MATHUES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Parsons et al. Oct. 26, 1943 

